[ONOS-7993] fix little bugs about finding line-side port's SIP.
[ONOS-7993] fix little bugs about finding line-side port's SIP.

Change-Id: I392bdd5f23172cc53534374a3f867cba0b8f66bc

oplinkoms/onos,gkatsikas/onos,oplinkoms/onos,oplinkoms/onos,oplinkoms/onos,opennetworkinglab/onos,oplinkoms/onos,gkatsikas/onos,gkatsikas/onos,oplinkoms/onos,gkatsikas/onos,opennetworkinglab/onos,opennetworkinglab/onos,oplinkoms/onos,opennetworkinglab/onos,gkatsikas/onos,opennetworkinglab/onos,opennetworkinglab/onos,gkatsikas/onos